1. Field of the Invention
The present invention relates to a composite gas separation membrane, a gas separation module, a gas separation apparatus, and a gas separation method.
2. Description of the Related Art
A material formed of a polymer compound has gas permeability specific to the material. Based on this property, it is possible to cause selective permeation and separation out of a target gas component using a membrane formed of a specific polymer compound. As an industrial use aspect for this gas separation membrane related to the problem of global warming, separation and recovery from large-scale carbon dioxide sources with this gas separation membrane has been examined in thermal power plants, cement plants, or ironworks blast furnaces. Further, this membrane separation technique has been attracting attention as a means for solving environmental issues which can be achieved with relatively little energy. In addition, natural gas or biogas (from biological excrement, organic fertilizers, biodegradable substances, sewage, garbage, fermented agricultural crops, or gas generated due to anaerobic digestion) is mixed gas mainly containing methane and carbon dioxide, and a membrane separation method is being examined as a means for removing impurities contained in the carbon dioxide and the like (JP2007-297605A).
When natural gas is purified using the membrane separation method, excellent gas permeability and separation selectivity are required in order to efficiently perform separation and purification of gas. Various membrane materials have been examined in order to realize excellent gas permeability and separation selectivity, and a gas separation membrane using a polyimide resin has been examined as a means therefor. For example, Journal of Membrane Science (2003, 211, p 41 to 49) discloses that separation selectivity of a gas separation membrane is improved when a polyimide resin to which a polar group such as a carboxy group or a hydroxyl group is introduced is used.
In order to obtain a practical gas separation membrane, it is necessary to ensure sufficient gas permeability by making a gas separation layer thinner and sufficient gas separation selectivity is further required. A method of making a portion contributing to separation into a thin layer referred to as a dense layer or a skin layer by forming a polymer compound such as a polyimide resin into an asymmetric membrane using a phase separation method is known as a technique of forming a gas separation layer into a thin layer (for example, see U.S. Pat. No. 5,928,410).